Atomic Physics seminars

Fault-tolerant computation usually builds an error-correctable logical qubit by entangling several physical qubits. Even when it represents one quantum bit, this logical object occupies a higher-dimensional space. Andrea Morello discusses a different approach that stores quantum information directly in a naturally high-dimensional physical system. The system uses an antimony nucleus with spin I = 7/2 and an eight-dimensional Hilbert space. As a group-V donor, the atom can be implanted into a silicon nanoelectronic device. Its nuclear spin supports Schrödinger-cat states that serve as logical codewords, without constructing them from multiple entangled physical qubits. Encoding employs a generalized rotating frame made possible by modern FPGA signal generators, including the Quantum Machines OPX. The talk considers this control infrastructure as a route to quantum-computing hardware that uses fewer resources.

Fault-tolerant quantum computation must overcome complex control requirements and substantial error-correction overhead. This talk describes reconfigurable neutral-atom arrays in which optical tweezers coherently transport atoms, enabling any-to-any connectivity, high-fidelity programmable operations and mid-circuit processing in a zoned architecture. Parallel control, transversal operations and long-range connections support experiments ranging from precise quantum-scrambling simulations to a universal fault-tolerant processing architecture. Theoretical methods exploiting reconfigurable connectivity reduce error-correction overhead and suggest that useful large-scale computation could require as few as 10,000 atomic qubits. The discussion considers the prospects for realizing this approach in the near term.

Lawrence Cheuk presents experiments using laser-cooled polar molecules held in optical-tweezer arrays. Molecular internal states and electric-dipole interactions provide resources for quantum computation, simulation and precision measurement. The talk covers preparation, control and detection of individual molecules; two-qubit operations and deterministic molecular entanglement; and one-dimensional spin simulations. Those experiments examine how spin excitations move, form bound pairs and undergo coherent pair creation and removal. A second set of experiments generates molecular spin-squeezed states and uses spatially resolved measurements to investigate reduced measurement noise, bipartite entanglement and Einstein-Podolsky-Rosen steering. Preliminary progress toward larger arrays may also be discussed. The Donald R. Hamilton Colloquium takes place in Jadwin Hall A-10 at Princeton University.

James K. Thompson describes how photons repeatedly reflected inside an optical cavity can couple laser-cooled atoms. These collective interactions provide tools for both simulating many-body systems and improving precision measurements. The seminar examines ways to shape the coupling, including exchange and XYZ interactions, interactions involving three or four particles, dissipative processes and protection of coherence through a many-body energy gap. Applications include studying time-dependent phases of superconductors, increasing the sensitivity of matter-wave interferometers and advancing optical clocks. The organizer provides both an Ann Arbor venue and an online attendance option.

The superfluid fraction measures how much of a fluid supports frictionless motion. This seminar studies low-temperature systems in which external potentials tune that fraction and transport measurements quantify it. For an equilibrium, weakly interacting Bose condensate, the researchers also extract the fraction from a single density image. The approach offers a new measurement route for investigating recently realized supersolid phases.

Tracy Northup explains how interactions between trapped atomic ions and single photons transfer quantum information between matter and light. Atom–photon entanglement can connect distant ions, as demonstrated by a prototype linking calcium ions across 230 metres. The seminar considers how larger networks could support secure communications, distributed computation and connected quantum sensors.

Quantum networks require links between stored qubits and information carried by travelling waves. This lecture compares interfaces coupling atoms, spins and superconducting circuits to optical or acoustic signals. It also introduces quantum memories, the measurements used to assess their performance, recent experimental results and applications that combine communication with quantum processing.

Markus Aspelmeyer examines whether laboratory experiments can reveal how gravity interacts with quantum matter. Quantum optomechanics offers tools for controlling the motion of solid objects, potentially allowing gravitational sources to occupy spatial superpositions. The seminar reviews trapped-solid experiments, the challenges of detecting gravity at microscopic scales and the requirements for future tests of massive quantum systems.

Vibrations can destroy quantum coherence, but they can also carry useful quantum information. This lecture examines both roles of phonons, including methods for reducing unwanted coupling to solid-state qubits. It introduces optical control of mechanical motion in the quantum regime and discusses applications to precision sensing, connections between different quantum systems and fundamental physics.

Antoine Browaeys describes synthetic quantum matter assembled from individually trapped atoms. Optical tweezers arrange the particles, while laser excitation controls their interactions. These experiments explore collective quantum behaviour in regimes that challenge conventional numerical simulation. The seminar also explains how this research contributed to the development of the quantum-computing company Pasqal.

This lecture explains quantum processors built from neutral atoms and trapped ions. It covers individual-particle confinement, internal states used to encode information and interactions that generate entanglement. The discussion connects these physical ingredients to analogue quantum simulation and to early demonstrations of error-correction protocols for digital computation.

Gerhard Rempe explores how to create useful entanglement across many qubits. Individual atoms in an optical cavity generate photons with controllable graph-shaped entanglement patterns. The seminar examines the experimental challenge of producing these states on demand and their potential for photonic error correction, quantum computation and communication that tolerates photon loss.

Photonic quantum processors use interference between indistinguishable photons to manipulate information. This lecture reviews proposed architectures and experiments involving several dozen photons. It then examines measurement-based computation as a route toward larger systems, including highly entangled light, error correction, distributed processing and possible integration with spin qubits.

Audrey Bienfait describes experiments using superconducting qubits to generate and absorb individual surface-acoustic-wave phonons. These travelling vibrations transfer quantum states and entangle separated qubits. The seminar also covers entanglement between two phonons and an acoustic quantum-eraser experiment, illustrating how controlled sound waves can contribute to quantum connections and sensing.

Reliable photon sources are essential for optical quantum communication and computation. This lecture compares single-photon generation through nonlinear optical processes with controlled emission from individual atoms. It discusses performance, limitations and integration, then extends the comparison to sources of entangled photons and more elaborate quantum states of light.

Mete Atatüre examines semiconductor quantum dots as interfaces between photons, electron spins and ensembles of nuclear spins. Optical control can turn the nuclear environment from a source of noise into a useful quantum system. The seminar follows this progression through collective nuclear states toward a register capable of storing quantum information.

This lecture introduces decoherence through simple models of quantum systems exposed to environmental disturbances. It explains how electric or magnetic noise degrades superposition, how the effect is measured and how it can be reduced. The discussion relates these issues to the DiVincenzo requirements for quantum computers and compares major experimental platforms.

Valentina Parigi presents quantum networks that encode information in optical-field quadratures. Nonlinear parametric processes generate entanglement among many spectral and temporal modes. The seminar considers spatial, spectral and temporal multiplexing, methods for analysing Gaussian entanglement networks, and operations that introduce the non-Gaussian resources needed for quantum computation.

This lecture develops the harmonic-oscillator description of travelling quantum signals. It compares information encoded in individual photons with information encoded in field components, introduces methods for characterising optical quantum states and reviews enabling detectors. Two-photon examples illustrate how entanglement can be measured.

Defects in diamond provide optically readable electron spins that can sense magnetic fields under demanding conditions. This seminar connects nitrogen-vacancy centres to diamond growth and defect engineering, then examines sensing applications. A particular focus is the study of superconducting materials under high pressure using diamond-anvil cells.